performance properties of polymer modified asphalt …
TRANSCRIPT
PERFORMANCE PROPERTIES OF POLYMER MODIFIED ASPHALT (PMA)
BINDERS CONTAINING WAX ADDITIVES
by
Mithil Mazumder
A thesis submitted to the Graduate Council of
Texas State University in partial fulfillment
of the requirements for the degree of
Masters of Science
with a Major in Technology Management
December 2016
Committee Members:
Soon-Jae Lee, Chair
Vedaraman Sriraman
Anthony Torres
COPYRIGHT
by
Mithil Mazumder
2016
FAIR USE AND AUTHOR’S PERMISSION STATEMENT
Fair Use
This work is protected by the Copyright Laws of the United States (Public Law 94-553,
section 107). Consistent with fair use as defined in the Copyright Laws, brief quotations
from this material are allowed with proper acknowledgment. Use of this material for
financial gain without the author’s express written permission is not allowed.
Duplication Permission
As the copyright holder of this work I, Mithil Mazumder, authorize duplication of this
work, in whole or in part, for educational or scholarly purposes only.
DEDICATION
I would like to dedicate this to my mother, Shilpi Mazumder.
v
ACKNOWLEDGEMENTS
First of all, I would like to take this opportunity to express my appreciation and gratitude
towards my parents, Bhudeb Mazumder and Shilpi Mazumder, for their continuous
support, sacrifice, pray in order to shape my life. In addition, I would like to thank my
sister, Tusti Mazumder, for her encouragement to pursue higher studies.
I would like to express my sincere thanks to my academic advisor and mentor, Dr. Soon-
Jae Lee, for the academic and professional guidance and support he has provided me
throughout my graduate studies. He always encourage me to do my research and his
motivation help me to continue my research effectively. Not but the least I always
appreciate his patience to understand my situation.
I would also like to thank the other members of my thesis committee, Dr. Vedaraman
Sriraman, and Dr. Anthony Torres for their helpful assistance and advice.
I want to acknowledge Mr. Hyunhwan Kim, for his assistance and support during my
Master’s at Texas State University. He has always been supportive throughout my study.
Finally, I wish to acknowledge and thank the faculty and staffs in the Department of
Engineering Technology for their constant support throughout my study.
vi
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS .................................................................................................v
LIST OF TABLES ........................................................................................................... viii
LIST OF FIGURES .......................................................................................................... ix
ABSTRACT ....................................................................................................................... xi
CHAPTER
1. INTRODUCTION ..............................................................................................1
Background .................................................................................................1
Scope of the Study .......................................................................................3
2. LITERATURE REVIEW ....................................................................................5
Polymer Modified Asphalt Binder ..............................................................5
Styrene-Butadiene-Styrene ..........................................................................6
Warm Mix Asphalt ......................................................................................6
3. MATERIALS AND METHODS ........................................................................8
Materials .....................................................................................................9
Asphalt binder .................................................................................9
LEADCAP ....................................................................................10
Sasobit ...........................................................................................10
Addition of wax additives .............................................................11
Experimental Procedure ............................................................................12
Rotational Viscometer (RV) Test .................................................12
Dynamic Shear Rheometer (DSR) Test ........................................14
Bending Beam Rheometer (BBR) Test .........................................15
4. STATISTICAL ANALYSIS ............................................................................16
5. RESULTS .........................................................................................................17
vii
Rotational viscosity ...................................................................................17
DSR Test ...................................................................................................23
Rutting property ............................................................................23
Fatigue cracking property .............................................................27
BBR Test ...................................................................................................30
6. SUMMARY AND CONCLUSIONS ...............................................................33
REFERENCES .................................................................................................................35
viii
LIST OF TABLES
Table Page
3-1. Properties of base asphalt binder (PG 64-22) .............................................................10
3-2. Designation of binder and description ........................................................................11
5-1. Statistical analysis results of the viscosity value as a
function of binder and wax additives; (a) 135°C and (b) 120°C ................................22
5-2. Statistical analysis results of the G*/sin δ value as a
function of binder and wax additives at 64°C (a) No aging and (b) RTFO aging .....26
5-3. Statistical analysis results of the G*sin δ value as a
function of binder and wax additives at 25°C after RTFO + PAV ............................29
5-4. Statistical analysis results of the stiffness value as a
function of binder and wax additives at -12°C after RTFO + PAV ...........................32
6-1. Comprehensive data ...................................................................................................33
ix
LIST OF FIGURES
Figure Page
3-1. Flow chart of experimental design ...............................................................................9
3-2. LEADCAP ..................................................................................................................12
3-3. Sasobit ........................................................................................................................12
3-4. Rotational viscometer .................................................................................................13
3-5. Dynamic Shear Rheometer (DSR) .............................................................................14
3-6. Bending Beam Rheometer (BBR) ..............................................................................15
5-1. Viscosity of the binders with wax additives
(a) 135°C and (b) 120°C .............................................................................................19
5-2. Viscosity change of control binder during
240 minutes at 135°C .................................................................................................20
5-3. Viscosity change of PMA binder during
240 minutes at 135°C .................................................................................................20
5-4. Viscosity change of control binder during
240 minutes at 120°C .................................................................................................21
5-5. Viscosity change of PMA binder during
240 minutes at 120°C ................................................................................................21
5-6. G*/sin δ of the binders with wax additives (No aging);
(a) 64°C and (b) 76°C .................................................................................................24
5-7. G*/sin δ of the binders with wax additives (RTFO);
(a) 64°C and (b) 76°C .................................................................................................25
5-8. G*sin δ at 25°C of the binders with wax additives
(after RTFO+PAV) ......................................................................................................28
x
5-9. Stiffness at - 12°C of the binders with wax additives
(after RTFO+PAV) ......................................................................................................31
5-10. m-value at - 12°C of the binders with wax additives
(after RTFO+PAV) ......................................................................................................31
xi
ABSTRACT
The study presents an experimental evaluation of the rheological properties of
control and polymer modified asphalt (PMA) binders containing wax additives and a
comprehensive comparison between these two binder types. The control and PMA
binders with the additives were produced using two of the available warm asphalt
processes (i.e., LEADCAP and Sasobit) and then artificially short-term and long-term
aged using the rolling thin film oven (RTFO) and pressure aging vessel (PAV)
procedures. Superpave binder tests were carried out on the binders through the rotational
viscometer (RV), the dynamic shear rheometer (DSR), and the bending beam rheometer
(BBR). In general the results of this study indicated that (1) the addition of wax additives
into the control and PMA binders decreases the viscosity, as expected; (2) the reduction
in viscosity was quite similar for both the binders with wax additives; (3) the percentage
increase of rutting resistance due to the additives was much higher for the control binder,
compared to the PMA binder; (4) both the control and PMA binders showed the similar
trends in terms of fatigue cracking and low temperature cracking behavior after the
addition of wax additives.
1
1. INTRODUCTION
Background
According to Environmental Protection Agency (EPA) in 2013, direct industrial
greenhouse gas emissions accounted for approximately 21% of the total emissions in the
United States, making it the third largest contributor, after the Electricity and
Transportation sectors due to a rise in population, economic growth, the fluctuating price
of energy, technological changes and many other factors. The paving industry has its own
share of emission concerns with its use of hot mix asphalt (HMA), with the major source
coming from the production facility. HMA plants, regardless of its manufacturing
technique (drum or batch) emit between 56,000 lbs/yr and 83,000 lbs/yr, depending on
their fuel type (natural gas, oil, etc) (USEPA 2000). As a result, warm mix asphalt
(WMA) technologies have been introduced to reduce the mixing and compaction
temperatures for asphalt mixtures as a means of reducing production cost, energy, and
most importantly pollutant emissions.
In order to improve the quality of asphalt pavements, the asphalt industry incorporated
polymers into asphalt as a way to mitigate the major causes for asphalt pavement failures,
including permanent deformation at high temperatures and cracking at low temperatures
(Chen et al. 2002; Li et al. 1998). When a polymer and virgin asphalt are blended, the
polymer strands absorb part of the low molecular weight oil fraction of the virgin asphalt
and become swollen. Of the polymer modifiers, styrene butadiene styrene (SBS)
originally developed by Shell Chemical Co. is widely used in the majority of the asphalt
binder industry and probably the most appropriate polymer for asphalt modification
2
(Lavin 2003; Becker et al. 2001). SBS creates a three dimensional network within virgin
asphalt phase resulting in excellent bonding strength to aggregates, which leads to a
durable and long lasting pavement (Kim 2003; Adedeji et al. 1996). According to Becker
et al., (2001), it is the most appropriate and used polymer for asphalt modification,
followed by reclaimed tire rubber. It is the formation of critical network between the
binder and SBS that increases the complex modulus, resulting the increase in rutting
resistance. In 2004, Florida Department of Transportation and FHWA report that SBS
benefited the cracking resistance by reducing the rate of micro-damage accumulation
(Roque et al., 2004).
Due to high viscosity and improved binder coating, polymer modified asphalt (PMA)
pavements have better pavement performance under high traffic applications. Polymer
modifications are becoming important factors in paving industry due to their proven
effects such as better resistance to rutting, fatigue damage, stripping, and thermal
cracking in asphalt pavements (Wekumbura et al. 2007; Punith 2005; Chen et al. 2002).
However, there have been difficulties in workability of PMA because of high viscosity of
the modified binders and concern about the health issues due to high level of toxic fumes
and continuous exposure of workers to high temperatures during paving operations. Also,
high temperature can thermally degrade the polymer as well as cause high economic cost
due to the increased fuel consumption (Roque et al. 2005; Budija et al. 2004; Zubeck et
al. 2003; Newcomb, 2006).
WMA technologies allow significant reduction of mixing and compaction temperatures
of asphalt mixes using proprietary chemicals. In addition, the WMA provides better
working condition based on reduction in emissions in asphalt plants and fields, and there
3
are many other promising benefits including less fuel consumption, longer paving
seasons, longer hauling distances, earlier traffic opening, reduced binder aging, and
reduced cracking (Akisetty et al. 2009; Button et al. 2007; D’Angelo et al. 2008; Gandhi
2007; Hurley and Prowell 2005; Hurley and Prowell 2006; Kim et al. 2013). WMA
technology can be used as a method of reducing the heat requirement for pavement
operations while at the same time maintaining the integrity of the PMA binder.
Scope of the Study
The objective of this study is to investigate the rheological properties of PMA binders
containing wax additives through Superpave binder tests. Control binders with wax
additives were used to compare with the PMA binders. The warm PMA binders were
produced with two commercial wax additives, LEADCAP and Sasobit, and artificially
aged using rolling thin film oven (RTFO) and pressure aging vessel (PAV) procedures.
The viscosity properties for the binders were evaluated in the original state through
rotational viscometer (RV) test using different testing temperatures (135°C and 120°C)
and periods (30, 120, and 240 minutes). Rutting resistance properties in the original state
and after RTFO aging as well as the fatigue cracking properties at intermediate
temperature after RTFO+PAV aging methods were evaluated by dynamic shear rheometer
(DSR) test. Low temperature cracking properties after RTFO+PAV procedures were
evaluated by bending beam rheometer (BBR) test. Figure 3-1 illustrates a flow chart of
the experimental design used in this study. Most of the studies investigated the
rheological properties of PMA binder by incorporating sasobit into the binder. Based on
this review, it appears that the addition of LEADCAP into the PMA binder and a
4
comprehensive comparison between the two binder types (control and PMA) with two
available wax additives (LEADCAP and sasobit) in terms of compatibility has not been
reported in the previous study. This study can provide a substantial body of knowledge on
such observations which may be of interest to the asphalt industry.
5
2. LITERATURE REVIEW
Polymer Modified Asphalt Binder
Asphalt modification using natural and synthetic polymers was patented in early 1843
(Thompson et al., 1979). Europe was more interested in the use of modified asphalt due
to its long term impact rather than its higher initial costs. Due to the high initial cost of
polymer modified asphalt (PMA), the use of PMA was limited in the United States (US).
But later in the mid-1980s European technologies were adopted in the US due to the
awareness for the long term economic impact. Polymers that have been used to modify
the asphalt binder include styrene-butadiene-styrene (SBS), styrene-butadiene-rubber
(SBR), ethylene vinyl acetate (EVA), polyethylene, and others (Yildirim, 2007). A
survey conducted by state departments of transportation in 1997 concluded that 47 states
out of 50 would like to start using modified binders in the future and 35 states of them
would use greater amounts (Bahia et al., 1997). In 2003, a US Army Corps of
Engineering study reports that for long term benefit in terms of economic and durability it
is beneficial to have such pavement built with modified asphalt that can resist multiple
distresses (Partl et al., 2003). In 2003, Newcomb claims that increasing content of
polymer modified binders at the bottom of the asphalt layer can increase the fatigue limit
of the pavement (Newcomb et al., 2003). Polymer modified binders should have the
following desirable characteristics: greater elastic recovery, a higher softening point,
greater viscosity, cohesive strength and ductility (Yildirim, 2007).
6
Styrene-Butadiene-Styrene (SBS)
Styrene-Butadiene-Styrene (SBS) is a block copolymer which can increase the elasticity
of asphalt. According to Becker et al., (2001), it is the most appropriate and used polymer
for asphalt modification, followed by reclaimed tire rubber. It is the formation of critical
network between the binder and SBS that increases the complex modulus, resulting the
increase in rutting resistance. In 2004, Florida Department of Transportation and FHWA
report that SBS benefited the cracking resistance by reducing the rate of micro-damage
accumulation (Roque et al., 2004). However, the addition of SBS has some drawbacks in
terms of economic and technical limits. It is capable to increase the low temperature
flexibility but some authors report that a decrease in strength and resistance to penetration
is observed at higher temperature (Yildirim et al., 2007).
Warm Mix Asphalt
Warm mix asphalt (WMA) is produced and spread at lower temperatures than HMA.
HMA is manufactured at 150-190°C whereas warm mix asphalt and half warm mix
asphalt produced at 100-140°C and 60-100°C, respectively (AAPA, 2001). This is the
result of adding organic additives, chemical additives and water based or water
containing foaming process. These additives are categorized into three parts (i) foaming
processes (divided into water-containing and water based process); (ii) addition of
organic additives (Fischer-Tropsch synthesis wax, fatty acid amides, and Montan wax);
(iii) addition of chemical additives (usually emulsification agents or polymers). Several
studies have been performed on the incorporation of wax additives into the PMA binder
(Edwards et al. 2010; Butt et al. 2010; Jamshidi et al. 2012, 2013; Kantipong et al. 2007,
7
2008; Kim et al. 2007, 2010, 2011, 2012; Susana et al. 2008; Hurley and Prowell, 2005).
It is evident from these studies that there are significant environmental benefits of using
WMA. It reduces the asphalt plant emission and fumes and energy consumption which is
beneficial for the environment as well as for the workers. Also, it is possible to add
recycle scrap tires into WMA. This way the industry can produce rubberized asphalt
mixtures which can reduce the mixing and compaction temperature as well as extending
the performance of the pavement.
8
3. MATERIALS AND METHODS
Chapter 3 provides descriptions of the materials included in this study as well as the
procedures used to accomplish the research objectives. Figure 3-1 illustrates the flow
chart of experimental design followed during this research. This chart provides a holistic
research process containing artificial aging process and specific test equipment to
evaluate each property of asphalt binder. This experimental plan was selected to examine
the effects of several variables on control binders and PMA binders with wax additives.
The summary below shows full names and the abbreviation used in this study.
PG: Performance Grade
64-22: The binder meets the high temperature properties upto 64°C and low temperature
properties down to -22°C
76-22: The binder meets the high temperature properties upto 76°C and low temperature
properties down to -22°C
G*: Complex shear modulus and δ : Sine of the phase angle
PMA: Polymer Modified Asphalt
RTFO: Rolling Thin Film Oven
PAV: Pressure Aging Vessel
RV: Rotation Viscometer
DSR: Dynamic Shear Rheometer
BBR: Bending Beam Rheometer
9
Binder with
LEADCAP
(b)
Control binder
(a)
Binder with
Sasobit
(c)
PG64-22
PG76-22
Same Testing Procedures
as (b)
Same Testing Procedures
as (b)
Artificial short-term aging
procedure:
RTFO
No AgingArtificial short-term and
long-term aging procedures:
RTFO + PAV
DSR:
G*/sin δ Rotational viscometer:
Viscosity
DSR:
G*/sin δ
DSR:
G*/sin δ
BBR:
Stiffness
m-value
Figure 3-1. Flow chart of experimental design
Materials
Asphalt binder
Performance grade (PG) 64-22 asphalt base binder and PMA binders containing SBS
(approximately 3% by the weight of binder) were used in this study. Characteristics of the
asphalt binder are presented in Table 3-1.
10
Table 3-1. Properties of base asphalt binder (PG 64-22)
Aging states Test properties PG 64-22
(unmodified)
PG 76-22
(SBS modified)
Unaged binder
Viscosity @ 135°C (cP) 531 3244
G*/sin δ @ 64°C (kPa) 1.4 5.9
G*/sin δ @ 76°C (kPa) - 1.9
RTFO aged residual
G*/sin δ @ 64°C (kPa) 2.5 13.7
G*/sin δ @ 76°C (kPa) - 3.3
RTFO+PAV
Aged residual
G*sin δ @ 25°C (kPa) 2558 3650
Stiffness @ -12°C (MPa) 287 285
m-value @ -12°C 0.307 0.302
LEADCAP
The LEADCAP is an organic additive of a wax-based composition that includes crystal
controller and artificial materials. The wax used in LEADCAP additive has about 110°C
melting point, so the LEADCAP in asphalt binder at 130°C (Yang et al., 2012). It is to
adjust crystalline degree of wax material at the low temperature (Kim et al. 2013). Figure
3-2 shows LEADCAP used in this study.
Sasobit
Sasobit is a product of Sasol Wax and a Fischer-Tropsch (FT) wax. It is a long chain
aliphatic hydrocarbon obtained from coal gasification using the Fischer-Tropsch. It is
completely melted into the asphalt binder at a temperature in excess of 115°C which can
11
reduce the binder viscosity. After crystallization, it forms a lattice structure in the binder
that is the basis of the structural stability of the binder containing Sasobit (Sasol wax).
Figure 3-3 shows Sasobit used in this study.
Addition of wax additives
LEADCAP and Sasobit were used in this study for producing the warm binders. The
process involved the addition of two wax additives at specified concentration (1.5% by
weight of the binder) followed by a hand mixing for 1 minute at 170°C in order to
achieve consistent mixing.
Binder aging processes were then conducted by rolling thin film oven (RTFO) for 85
minutes at 163°C (ASTM D 2872) and pressure aging vessel (PAV) for 20 hours at 100°C
(ASTM D 6251). Table 3-2 explains the arrangement of binders with wax additives used
in this study.
Table 3-2 Designation of binder and description
Designation Description Method
Control Base binder -
Control + L Binder with 1.5% LEADCAP Hand mix
Control + S Binder with 1.5% Sasobit Hand mix
PMA PMA binder -
PMA + L PMA with 1.5% LEADCAP Hand mix
PMA + S PMA with 1.5% Sasobit Hand mix
12
Figure 3-2. LEADCAP
Figure 3-3. Sasobit
Experimental Procedure
Rotational Viscometer (RV) Test
A Brookfield rotational viscometer was utilized to determine the viscosity of each binder
at 135°C per AASHTO T 316 and at 120°C (the mixing temperature generally used for
warm mix asphalt). The viscosity is determined by measuring the torque required to
13
maintain a constant rotational speed of a cylindrical spindle while submerged in an
asphalt binder sample at a constant temperature. A 10.5g binder sample was tested with a
number 27 cylindrical spindle (10.5 mL) rotated with constant speed (20 rpm) for PMA
binder. The control binders without modifiers were tested in accordance with the same
procedure except an 8.5g sample was tested with a number 21 spindle (8mL). Three
testing periods (i.e., 30, 120, and 240 minutes) were used to evaluate the viscosity change
in different testing periods.
According to the Superpave binder test, the maximum viscosity of unaged asphalt binder
is 3.0 Pa-s (3000 cP). Figure 3-4 shows a picture of a rotational viscometer.
Figure 3-4. Rotational viscometer
14
Dynamic Shear Rheometer (DSR) Test
The high temperature rheological properties of each binder were measured using a
dynamic shear rheometer (DSR) per AASHTO T 315. In the DSR test, the original
binders and RTFO residual binders, which were tested with a 25 mm spindle at 64°C and
76°C and parallel plate and the binders (RTFO+PAV residual) were tested using an 8
mm parallel plate at 25°C. Figure 3-5 shows a DSR testing apparatus used in this study.
In the DSR test, the binders (Original, RTFO residual, and RTFO + PAV residual) were
tested at a frequency of 10 radians per second which is equal to approximately 1.59 Hz.
Each asphalt binder both in the original state (unaged) and short-time aged state used to
determine the G*/sin δ. The G*sin δ at intermediate temperature was measured to
evaluate the fatigue cracking property for RTFO+PAV residual binders.
Figure 3-5. Dynamic Shear Rheometer (DSR)
15
Bending Beam Rheometer (BBR) Test
BBR test was used to evaluate crack property at low temperature according to AASHTO
T 313. The stiffness was measured from -12°C. Figure 3-6 shows a BBR testing
apparatus used in this study.
The BBR test was conducted on asphalt beams (125 × 6.35 × 12.7 mm) at -12°C, and the
creep stiffness (S) of the binder was measured at a loading time of 60s. A constant load of
100g was then applied to the beam of the binder, which was supported at both ends, and
the deflection of center point was measured continuously. Testing was performed on
RTFO+PAV residual samples.
Figure 3-6. Bending Beam Rheometer (BBR)
16
4. STATISTICAL ANALYSIS
A statistical analysis was performed using the Statistical Analysis System (SAS) program
to conduct an analysis of variance (ANOVA) and Fisher’s Least Significant Difference
(LSD) comparison with an α = 0.05. The primary variables included the wax types
(Control, LEADCAP, and Sasobit) and the binder types (Control and PMA).
The ANOVA was performed first to determine whether significant differences among
sample means existed. In the analyses of this study, the significance level was .95 (α =
0.05), indicating that each finding had a 95% chance of being true. Upon determining that
there were differences among sample means using the ANOVA, the LSD was then
calculated. The LSD is defined as the observed differences between two sample means
necessary to declare the corresponding population means difference. Once the LSD was
calculated, all pairs of sample means were compared. If the difference between two
sample means was greater than or equal to the LSD, the population means were declared
to be statistically different [Ott, 2001].
17
5. RESULTS
Rotational viscosity
The viscosity of asphalt binder at high temperature is considered to be an important
property to decide working temperature because it reflects the binder’s ability to be
pumped through an asphalt plant, thoroughly coat aggregate in a HMA mixture, and be
placed and compacted to form a new pavement surface (Asphalt Institute, 2003). Figure
5-1 shows the standard RV test results for all binders used in this study. It is clear that the
addition of SBS into the asphalt binder greatly increases the binder viscosity, as expected.
The results indicate that the addition of wax additives results in decreasing the mixing
and compaction temperatures for all binders containing the additives. LEADCAP and
Sasobit were observed to be effective to reduce the viscosity of control binder by 9.7%
and 13.6%, respectively and this reduction in viscosity was remained similar in both
testing temperatures. Sasobit has significant effect in reducing the viscosity of PMA
binder (Edwards et al. 2010; Hurley and Prowell 2005; Kim 2007; Kim et al. 2010, 2011,
2012; Jamshidi et al. 2012, 2013; Kantipong et al. 2007; Susana et al. 2008; Kim et al.
2014). The reduction in viscosity of PMA binder at 135°C with Sasobit was
approximately twice compared to the PMA binder with LEADCAP whereas at 120°C
decreasing rate was 13.3% and 10.5% by the addition of Sasobit and LEADCAP,
respectively. The viscosity values of PMA binders at 120°C do not meet the current
maximum requirements set forth by Superpave (i.e., 3,000 cP). Although at 135°C the
PMA binder shows the higher values than the requirement, whereas the PMA binder with
18
wax additives satisfies the requirement. Similar decreasing trend and rate of viscosity
were observed at both temperatures for the control and PMA binders with wax additives.
One of the benefits of WMA binder is a longer hauling distance and period. The hauling
management of asphalt mixture usually depends on the binder viscosity. The viscosity
test was performed for 240 minutes to evaluate the longer hauling management of control
and PMA binders. This is demonstrated in Figures 5-2 and 5-3, which depict the time
versus viscosity curve for 240 minutes at 135°C. As expected, PMA binders exhibited
much higher viscosity values than control binders. According to Figure 5-2, the viscosity
values of control binders were stabilized between 20 and 40 minutes and the viscosity
values were found to have little change for the whole testing period. On the other hand,
the viscosity of PMA binders steadily increased approximately after 30 to 40 minutes.
The viscosity test was performed at the lower temperature of 120°C that is generally used
for WMA. The viscosity changes for 240 minutes were illustrated in Figures 5-4 and 5-5
at 120°C. Generally, there was no considerable viscosity change at 120°C, similar to
135°C. However, the PMA binders showed much higher viscosity than the current
requirement at 120°C. The viscosity curves of PMA binders containing LEADCAP or
Sasobit were found to have increasing trends over the increasing periods of time. Also,
the differences between PMA binder and PMA binders with the additives were higher
compared to those at 135°C.
19
(a)
(b)
Figure 5-1. Viscosity of the binders with wax additives; (a) 135°C and (b) 120°C
20
Figure 5-2. Viscosity change of control binder during 240 minutes at 135°C
Figure 5-3. Viscosity change of PMA binder during 240 minutes at 135°C
21
Figure 5-4. Viscosity change of control binder during 240 minutes at 120°C
Figure 5-5. Viscosity change of PMA binder during 240 minutes at 120°C
22
Table 5-1. Statistical analysis results of the viscosity value as a function of binder
and wax additives; (a) 135°C and (b) 120°C
(a)
Viscosity
PG 64-22 PG 76-22
Control Control +
L Control + S PMA PMA + L PMA + S
Control - S S S S S
Control + L - N S S S
Control + S - S S S
PMA - S S
PMA + L - S
PMA + S -
(b)
Viscosity
PG 64-22 PG 76-22
Control Control +
L Control + S PMA PMA + L PMA + S
Control - S S S S S
Control + L - N S S S
Control + S - S S S
PMA - S S
PMA + L - S
PMA + S -
N: non-significant S: significant
The statistical significance of the change in the viscosity as a function of WMA additive
and binder types was examined and results are shown in Table 5-1. The data indicated
23
that the binder types have a significant effect on the viscosity value at both testing
temperatures (135°C and 120°C). In most cases (except for control binder: Control+L vs.
Control+S), the results showed that, within each binder type, the binders have a
significant difference in the viscosity depending on the WMA additive.
DSR Test
Rutting property (G*/sin δ)
The higher G*/sin δ values from the DSR test indicate that the binders are less
susceptible to rutting or permanent deformation at high pavement temperature (Asphalt
Institute, 2003). The G*/sin δ values of binders in original state and after short time aging
were measured at 64°C and 76°C. The results are shown in Figures 5-6 and 5-7. In
general, the PMA binders resulted in the higher G*/sin δ than the control binders
regardless of aging state. However, the percentage improvement of rutting resistance due
to the addition of wax additives were observed much higher for control binders compared
to PMA binders. The reason might be the PMA binder was already modified with SBS
for high temperature performance so the addition of wax additives has less effect
compared to the unmodified control binder. The use of wax additives into binders was
observed to increase the G*/sin δ values in both aging states except for PMA binder with
LEADCAP at 64°C during RTFO aging process.
The binders with Sasobit showed the highest values within each binder type (Control
binder or PMA binder) regardless of aging and temperature which is due to the presence
of wax crystals (Edwards and Redelins 2003; Edwards et al. 2006). This finding is
24
consistent with the previous observations (Jamshidi et al. 2013; Kim et al. 2010, 2011,
2012; Kantipong et al. 2008; Kim 2007).
(a)
(b)
Figure 5-6. G*/sin δ of the binders with wax additives (No aging);
(a) 64°C and (b) 76°C
25
(a)
(b)
Figure 5-7. G*/sin δ of the binders with wax additives (RTFO);
(a) 64°C and (b) 76°C
26
Table 5-2. Statistical analysis results of the G*/sin δ value as a function of binder and
wax additives at 64°C (a) No aging and (b) RTFO aging
(a)
G*/sin δ
PG 64-22 PG 76-22
Control Control +
L Control + S PMA PMA + L PMA + S
Control - S S S S S
Control +
L - N S S S
Control + S - S S S
PMA - N N
PMA + L - N
PMA + S -
(b)
G*/sin δ
PG 64-22 PG 76-22
Control Control +
L Control + S PMA PMA + L PMA + S
Control - S S S S S
Control +
L - N S S S
Control + S - S S S
PMA - N S
PMA + L - S
PMA + S -
N: non-significant S: significant
27
It means that the wax additive of Sasobit has a positive effect on the rutting resistance at
high temperature due to the presence of wax crystals in the binders which causes an
increase in the complex modulus of the binders. In short, both the wax additives and the
SBS polymer play a significant role in improving rutting resistance. The statistical results
of the change in the G*/sin δ values for no aging and RTFO aging at 64°C are shown in
Table 5-2. Regardless of aging, the data indicated that the binder types have a significant
effect on the G*/sin δ values. For no aging, the differences between control binder and
the control binder containing LEADCAP or Sasobit are statistically significant. For
RTFO aging, the PMA binder with Sasobit was found to be significantly different in the
G*/sin δ value when compared to other PMA binders.
Fatigue cracking property (intermediate failure)
The product of the complex shear modulus G* and the sine of the phase angle, δ, is used
in Superpave binder specification to help control the fatigue of asphalt pavements. The
lower values of G*sin δ are considered desirable attributes from the standpoint of
resistance of fatigue cracking (Asphalt Institute, 2003). The G*sin δ values of the binders
(RTFO+PAV residual) were measured using the DSR at 25°C and the results are
illustrated in Figure 5-8. The PMA binder exhibited the higher G*sin δ values than the
control binder, indicating that the SBS polymer modification does not improve the
resistance for fatigue cracking. The binders with Sasobit showed the highest values
within each binder type (Control binder or PMA binder) which is consistent with the
previous finding (Kim et al. 2010). However, the addition of LEADCAP into control and
PMA binders reduced the G*sin δ values by 11% and 27.4%, respectively. It means that
28
the wax additive LEADCAP has a positive effect on the cracking resistance at
intermediate temperature. Also, all the values satisfied the maximum requirements of
5,000 kPa by Superpave.
The statistical significance of the change in the G*sin δ value as a function of WMA
additive and binder types was examined and results are shown in Table 5-3. The results
showed that binder types have a significant effect in the G*sin δ value, except for PMA
binder containing LEADCAP. The differences between control binder and the control
binder with LEADCAP or Sasobit were statistically insignificant within whereas the
differences between PMA binder and the PMA binder with the wax additives were
statistically significant.
Figure 5-8. G*sin δ at 25°C of the binders with wax additives (after RTFO+PAV)
29
Table 5-3. Statistical analysis results of the G*sin δ value as a function of binder and wax
additives at 25°C after RTFO + PAV
G*sin δ
PG 64-22 PG 76-22
Control Control +
L Control + S PMA PMA + L PMA + S
Control - N N S N S
Control +
L - S S N S
Control + S - S N S
PMA - S S
PMA + L - S
PMA + S -
N: non-significant S: significant
30
BBR Test
Superpave asphalt binder specification includes a maximum value of 300 MPa for creep
stiffness and the decrease in stiffness is expected to lead to smaller tensile stress in the
asphalt binder and less chance for low temperature (Asphalt Institute, 2003). From the
BBR tests at -12°C, the stiffness and m-value of control and PMA binders with wax
additives (RTFO+PAV residual) were calculated and the results are shown in Figures 5-9
and 5-10. After the RTFO+PAV aging processes, the control and PMA binder stiffness
values at -12°C are measured to be 287 MPa and 285 MPa, respectively. The PMA
binder with LEADCAP is found to have the lowest stiffness values of 265 MPa, which is
approximately 7% lower than the PMA binder stiffness. The binders with sasobit was
found to have highest stiffness value within each binder type (Edwards et al. 2010; Kim
et al. 2010; Kim et al. 2016). All the control and PMA binders, except for the binders
with 1.5% Sasobit, satisfied the requirement set forth by Superpave (maximum 300
MPa). In general, the use of SBS polymer to modify the asphalt binder in terms of
thermal cracking properties is observed to have little influence. However, the PMA
binder with LEADCAP is expected to have the best performance with regard to low
temperature cracking resistance, among six binder types used in the study. Also, G*sin δ
values at 25°C and the stiffness values of control and PMA binders with wax additives
were found to have similar trend.
31
Figure 5-9. Stiffness at - 12°C of the binders with wax additives (after RTFO+PAV)
Figure 5-10. m-value at - 12°C of the binders with wax additives (after RTFO+PAV)
32
Table 5-4. Statistical analysis results of the stiffness value as a function of binder and wax
additives at -12°C after RTFO + PAV
Stiffness
PG 64-22 PG 76-22
Control Control +
L Control + S PMA PMA + L PMA + S
Control - N S N S N
Control + L - S N N S
Control + S - S S S
PMA - N S
PMA + L - S
PMA + S -
N: non-significant S: significant
The statistical results of the change in the stiffness value are shown in Table 5-4. In
general, the data indicated that within each binder type, the differences between the
binder and the binder containing LEADCAP are statistically insignificant. For both
binders, the wax types were found to have significant difference on the stiffness values.
33
6. SUMMARY AND CONCLUSIONS
To investigate the performance properties of control and PMA binders with wax
additives, warm PMA binders were produced using two wax additives, LEADCAP and
Sasobit, and artificially short-term and long-term aged in the laboratory. A series of
Superpave binder tests were carried out using the rotational viscometer, the DSR, and the
BBR to evaluate various performance properties (viscosity, rutting, fatigue cracking, and
low temperature cracking) of the binders. Table 6-1 shows the comprehensive data for
this study. From the test results, the following findings were drawn for the materials used
in this study.
Table 6-1. Comprehensive data
Binders
Viscosity (cP) G*/sin δ
G*sin δ Stiffness
135°C 120°C Original RTFO
Control 531.2 1207.7 1.3 - 2.5 - 2550.0 287.0
Control+L 479.7 1088.8 1.8 - 3.6 - 2270.0 269.0
Control+S 459.0 1045.0 1.9 - 3.6 - 2987.0 333.0
PMA 3244.0 7658.0 5.9 1.9 13.7 3.3 3650.0 285.0
PMA+L 2994.0 6853.0 6.0 2.2 12.1 3.8 2650.0 265.0
PMA+S 2765.0 6639.0 6.5 2.7 16.9 4.1 4653.0 319.0
1) The addition of two wax additives into a control binder and PMA binders can
significantly decrease the viscosity at 135°C and 120°C and the reduction in viscosity
was quite similar for both binders.
34
2) The viscosity of control binders were stabilized between 20 and 40 minutes and
remained constant whereas the viscosity of PMA binders steadily increased after 30
to 40 minutes over the whole testing period at 135°C. The same trend was observed at
120°C.
3) Generally, both the additives were observed to be effective on increasing the rutting
resistance. Irrespective of the aging state (no aging and RTFO), it was found that the
control binders containing wax additives have the higher percentage improvement in
rutting resistance compared to the PMA binders with the additives.
4) From the DSR test at intermediate temperature, the binders with Sasobit were
observed to have higher G*sin δ values, meaning that they are less resistant to fatigue
cracking. Whereas, the addition of LEADCAP significantly reduced the G*sin δ
values, suggesting that the use of LEADCAP was useful to improve the fatigue
cracking resistance. These trends were similar for both the control and PMA binders.
5) Between these two wax additives, LEADCAP is better than Sasobit in terms of
resistance to fatigue and low temperature cracking. On the other hand, for rutting
resistance, Sasobit performs better than LEADCAP.
6) The binders with Sasobit were found to have significantly higher stiffness values
which relate to possible lower resistance on low temperature cracking. However, the
addition of LEADCAP significantly reduced the stiffness values. Both the binders
were found to have the similar trend in stiffness values. Also, the use of SBS polymer
seemed to have little effect on the thermal cracking behavior. It is recommended to
conduct a field study to generalize these findings with the field behavior.
35
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